# Drawing a Plane

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Hello,

I've been trying to add support for planes, grids, call them what you will, in my engine.

I've been mostly successful, except for the problem illustrated by this screenshot:

I have no idea why this would occur.

 private SurviveMesh ReadPlane(BeginMode primType, SurvivePrimitiveParam par) { SurviveMesh mesh = new SurviveMesh(); Vector3d[] vertex = new Vector3d[4]; Vector3d[] normal = new Vector3d[4]; Vector2d[] texCoord = new Vector2d[4]; int k; for (k = 0; k < 4; k++) { vertex[k] = new Vector3d(); normal[k] = new Vector3d(); texCoord[k] = new Vector2d(); } double xmin = par.param[0]; double xmax = par.param[1]; double step = par.param[2]; uint numVerts = (uint)((xmax - xmin) / step) * 8; mesh.BeginMesh(primType, numVerts + 4); for (double x = xmin; x <= xmax; x += step) { vertex[0] = new Vector3d(x, -0.55, xmax); normal[0] = new Vector3d(0, 1, 0); texCoord[0] = new Vector2d(x / xmax, 1.0); vertex[1] = new Vector3d(x, -0.55, xmin); normal[1] = new Vector3d(0, 1, 0); texCoord[1] = new Vector2d(x / xmax, 0.0); vertex[2] = new Vector3d(xmax, -0.55, x); normal[2] = new Vector3d(0, 1, 0); texCoord[2] = new Vector2d(1.0, x / xmax); vertex[3] = new Vector3d(xmin, -0.55, x); normal[3] = new Vector3d(0, 1, 0); texCoord[3] = new Vector2d(0.0, x / xmax); mesh.AddTriangle(vertex, normal, texCoord); vertex[0] = vertex[1]; normal[0] = normal[1]; texCoord[0] = texCoord[1]; vertex[1] = vertex[3]; normal[1] = normal[3]; texCoord[1] = texCoord[3]; mesh.AddTriangle(vertex, normal, texCoord); } mesh.End(); mesh.Filename = par.filename; logger.FormatLine(SurviveLogger.InfoLogging, "Plane \"{0}\" created successfully.", mesh.Filename); logger.FormatLine(SurviveLogger.DetailedLogging, "\"{0}\" has {1} vertices and {2} faces.", mesh.Filename, mesh.NumVerts, mesh.NumFaces); return mesh; } 

Note: I think I'm telling BeginMesh an excessive amount of vertices, but if I scale by 4 instead of 8 like I think I should, it throws an IndexOutOfRangeException.

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You appear to be trying to create a grid by using two sets of intersecting lines. However, you're using triangles instead of line segments. This is why you have those diagonal lines streaking back across the map; those are the third side of each of those triangles.

Second, because you're using triangles, assuming mesh.addTriangle() uses only the first three array elements from the data you pass it and producing a triangle list (as opposed to a triangle strip or fan), you're generating 6 vertices per iteration step, not either 4 or 8.

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